Boot device not found/Hard disk does not exist.

I have a Presario CQ57 Note book with windows 7 home premium. My computer suddenly shut down. When I restarted it, there was a black screen that
says ,' Boot device not found
Please install an operation system on your hard disk.
Hard Disk (3F0)
F2 System Diagnostics'
Can someone please, please help me with this issue? I don't know much about computers.
Thank you :(